Across
- 2. Organs in mammals that produce milk for offspring.
- 7. Eggs with a protective shell and internal membranes, found in reptiles and birds.
- 9. Flexible connective tissue found in the skeletons of some fish.
- 12. Gas-filled organ that helps bony fish control buoyancy.
- 13. Body plan arranged around a central axis, found in cnidarians.
- 15. Sessile, generally asexual stage in the life cycle of cnidarians.
- 17. Organisms that rely on external heat sources, like most fish and reptiles.
- 18. Process of shedding the outer covering, such as an exoskeleton.
- 19. Internal skeleton, characteristic of echinoderms and vertebrates.
- 20. Network of water-filled canals in echinoderms.
Down
- 1. Organisms that generate their own body heat, like birds and mammals.
- 3. Describing organisms that live on the bottom of a body of water.
- 4. Animals without a backbone.
- 5. Hard, external supporting structure found in arthropods.
- 6. Body plan where only one line can divide the body into equal halves, found in many marine worms.
- 8. An organism with both male and female reproductive organs, like some sponges.
- 10. Lack of symmetry, characteristic of sponges.
- 11. Animals with a backbone.
- 14. A form of asexual reproduction in sponges.
- 16. Organ in placental mammals that nourishes the fetus.
- 21. Free-swimming, sexual stage in the life cycle of cnidarians.